Anything in the .40 size class. A buddy and I (he just builds now at 87) have used ours on several airplanes. We have found the Maggie 52s to be very reliable on a twin. Here are a few pictures of planes with our 2 Mag .52s.

My recommendations for twins after 25 of them
-Tune each engine individually and don't worry about syncing
-Set each one slightly rich. Never lean out to the peak-one will surely quit.
-Don't let your buddies tweak your engines.
-If the plane makes a goofy move, throttle immediately to idle, then come back in slowly with the power and rudder. You have probably lost an engine.
-Don't let your buddies mess with your engines.